Wifi goes off and I can't bring it back on unless I shut down and start again the laptop

I have upgraded my macbook to el capitan and after updating to the latest version 10.11.3 on 27 Jan 2016, I have problem connecting to the wifi!

My laptop is a macbook pro from mid 2010 with sad and

After a while surfing, wifi goes off and I can't bring it back on, no matter what. It's not a problem of not seeing my router, no wifi routers are detected.

The amount of time I stay connected varies each time, from upon starting to after 1 hour or so, by not doing anything in particular, surfing the web, looking stuff on finder etc.

Only after shutting down and starting it again it works, again for a while.

I have tried everything, I think!

Reset pram and sac, Removed plist files from /Library/Preferences/SystemConfiguration, turned bluetooth on and off, ran kext/disk utilities, created new location in wifi settings and everything else I've found online for wifi issues.

It was working ok for almost a month under el capitan.

Only thing I haven't tried so far is reinstalling the OS.

Can anyone please advise? Thanks in advance!